Apparatus for detecting explosive gases



June 12, 1951 R. POOLE 2,557,008

APPARATUS FOR DETECTING EXPLOSIVE GASES Filed Aug. 4, 1947 Patented June12, 1951 APPARATUS FOR DETECTING EXPLOSIVE GASES Ralph Poole, London,England Application August 4, 1947, Serial No. 765,985 In Great BritainFebruary 7, 1944 Section 1, Public Law 690, August 8, 1946 Patentexpires February 7, 1964 9 Claims.

My invention relates in general to apparatus for detecting the presenceof explosive, toxic, or other dangerous gases and, more particularly, toan apparatus of the type in which the gases to be tested are caused topass through a chamber containing an electrically heated filament whichforms part of a bridge circuit.

This application is a continuation in part of my application Serial No.523,380, filed February 21, 1944, now Patent No. 2,546,273.

In an apparatus of this type, the temperature of the heated filamentvaries with variations in the proportion of an explosive gas present inthe air or other gas mixture being tested because of the fact that theheated filament causes local combustion of the explosive gas. In someinstances, however, such variations in the temperature of the heatedfilament may be due to other causes, such as, for example, variations inthe thermal conductivity of the gases being tested resulting fromvariations in the proportion of the dangerous gas present therein. Ineither event, variations in the temperature of the filament may beindicated by a suitable electrical measuring instrument which formsanother part of the bridge circuit.

One of the difiiculties encountered with appa ratus of this type is thatif the gases being tested are permitted to impinge directly upon thefilament, or if they flow too rapidly through the space in which thefilament is mounted, the filament may be damaged, or at least may failto operate in a reliable manner. Accordingly, it has been foundnecessary to provide means for shielding the filament, and the provisionof an improved shielding means represents a primary object of myinvention.

More specifically, an object of the invention is to provide an apparatusof the foregoing general character having means for distributing theflow of the gases being tested in such a manner that they do not impingedirectly upon the filament and in such a manner that they fiow past thefilament relatively slowly.

Another object of the invention is to provide an apparatus having meansfor causing the gases being tested to flow into a space surrounding thefilament in a relatively thin, annular stream and to leave such space ina similar stream so that the gases do not impinge directly upon thefilament and so that the local velocity of the gases adjacent thefilament is relatively low.

A further object is to provide an apparatus of the character indicatedwherein the filament is mounted in the chamber on a removable s pporthaving baflies or flanges thereon which extend into close proximity witha wall of the chamber and cooperate therewith to cause the gases beingtested to enter and leave the space surrounding the filament inrelatively thin streams.

The flanges and the chamber are preferably circular so as to form narrowcircumferential slots through which the gases being tested must enterand leave the space in which the filament is disposed. Thus, the flangescooperate with the wall of the chamber to form a compartment whichcommunicates with the remainder of the chamber only through suchcircumferential slots so that the gases being tested cannot impingedirectly upon the filament.

The foregoing objects of my invention and the advantages suggestedthereby, together with various other objects and advantages which willbe evident hereinafter, may be attained through the employment of theexemplary embodiment which is illustrated in the accompanying drawingand which is described in detail hereinafter. Referring to the drawing:

Fig. 1 is a longitudinal sectional view of an apparatus embodying theinvention; and

Fig. 2 is an end view of a filament support forming part of theapparatus.

In the particular construction illustrated, the apparatus includes acasing or housing It having a cylindrical chamber 1 I therein and havinginlet and outlet passages 12 and I3 therein, which to a source of thegases to be tested, and the out let line may lead to a suitable point ofdischarge.

The chamber H may be closed by a cap I8 which is threadedly or otherwiseconnected to the housing I0 and which carries a filament sup port 19,the latter being provided with a flange 2!) at one end which is clampedbetween the cap 18 and the housing. Preferably, an annular sealingelement 2! is disposed between the flange 2n and the casing H] toprovide a fluid-tight seal. Pro jecting from the filament support I9 isa peg 22 which extends into a suitable opening in the easlng l0 andwhich retains the support with respect to the casing. Also projectingfrom the filament support I!) is another peg 24 which is inserted into anotch 25 in the casing to prevent rotation of the support.

The filament support comprises a plug-like end portion on which theflange 20 is formed, and

comprises a disc like end portion 26 which carries the pegs 22 and 25,these portions being connected by circumferentially spaced pins 21.Longitudinally spaced circular flanges 28 and 29 are formed on orsecured to the two end portions, respectively, of the filament supporti9, and a screen 3!! extends between the flanges 28 and 29, as bestshown in Fig. 1, the screen preferably being of circular cross section.It will be noted that the flanges 28 and 29 extend into close proximityto the circumferential wall of the chamber H so as to provide relativelynarrow circumferential slots 3! and 32 through which the gases beingtested are required to fiow, as will be discussed in more detailhereinafter.

Supported on suitable conductors 33 within the screen 38 is anelectrically heated detecting filament 34 connected in any appropriatemanner to suitable terminals, one of which is indicated by the numeral35, so that it can be connected in a bridge circuit. .Since the means bywhich the filament 34 is heated and the manner in which it may beconnected in a bridge circuit to obtain indications of variations in itstemperature are well known in the art, and since such components per seform no part of the present invention, they are not shown on thedrawing.

Considering the operation of my detecting apparatus, the inlet line Itmay be connected to a source of gases to be tested so that such gaseswill enter an inlet compartment at the right end of the chamber H, asviewed in Fig. 1, by way of the inlet line [3 and the inlet passage l2.From this inlet compartment, the gases must fiow through the narrowcircumferential slot 3| between the flange 29 and the circumferentialwall of the chamber H into the space surrounding the screen 39 in theform of a relatively thin, annular stream. The gases will then percolatethrough the screen 36 so as to come in contact with the detectingfilament 3 3 and, subsequently, will leave the space surrounding thefilament by again percolating through the screen and flowing through thecircumferential slot 32 provided by the flange 28 and the wall of thechamber II. It will be apparent that with this construction, the gasesbeing tested cannot impinge directly upon the detecting filament 34 and,moreover, must flow past the filament at a low velocity so that there isno tendency to damage the filament and so that a reliable indicationwill always be obtained.

It will be noted that with the particular construction illustrated, theentire filament support l9 may be removed readily for repair orreplacement when necessary by the simple expedient of unscrewing the capl8 and withdrawing the filament support from the chamber H as a unit,which is a feature of the invention.

Although I have disclosed an exemplary embodiment of my invention hereinfor purposes of illustration, it will be understood that variouschanges, modifications and substitutions may be incorporated thereinwithout necessarily departing from the spirit of the invention, and Ihereby reserve the right to all such changes, modifications andsubstitutions as properly come within the scope of the invention as setforth in the appended claims.

I claim as my invention:

1. In a gas testing apparatus, the combination of casing means having anelongated cavity therein and having inlet and outlet passages thereinrespectively communicating with opposite ends of said cavity; animperforate. inlet baffle in said cavity intermediate said inlet andoutlet passages and spaced from one end of said cavity to provide aninlet chamber communicating with said inlet passage, said inlet baffleextending into close proximity to but being spaced from the peripheralwall of said cavity so as to provide a narrow, peripheral inlet portthrough which a gas in said inlet chamber is required to flow to passsaid inlet balile; an imperforate outlet baflle in said cavityintermediate said inlet baffle and said outlet passage, said outletbafile being spaced from said inlet bafile to provide a compartmenttherebetween and being spaced from the other end of said cavity toprovide an outlet chamber communicating with said outlet passage, saidoutlet bafile extending into close proximity to but being spaced fromthe peripheral wall of said cavity so as to provide a narrow, peripheraloutlet port through which a gas in said compartment is required to flowto pass said outlet bafile and enter said outlet chamber; means forsupporting said baffies in said cavity; and a filament carried by saidsupporting means and disposed in said compartment intermediate saidbafiles.

2. A gas testing apparatus as set forth in claim 1 wherein said bafflescomprise annular flanges on said supporting means.

3. A gas testing apparatus as set forth in claim 1 including aforaminous Wall extending between said bafiles and encompassing saidfilament. 4. A gas testing apparatus as set forth in claim 1 whereinsaid cavity is of circular cross section and wherein said bafiies arecircular so that said ports are of annular configuration.

5. In a gas testing apparatus, the combination of casing means having anelongated cavity therein and having inlet and outlet passages thereinrespectively communicating with opposite ends of said cavity; animperforate inlet bafile in said cavity intermediate said inlet andoutlet passages and spaced from one end of said cavity to provide aninlet chamber communicating with said inlet passage, said inlet bafiieextending into close proximity to but being spaced from the peripheralwall of said cavity around the entire periphery of said inlet bafile soas to provide a narrow, continuous, peripheral inlet port through whicha gas in said inlet chamber is required to flow to pass said inletbafiie; removable means for supporting said inlet bafile in said cavity;and a filament carried by said removable supporting means and disposedon the lee side of said inlet baffle so as to be shielded from a gasstream flowing through said continous peripheral inlet port.

6. A gas testing apparatus as set forth in claim 5 wherein said cavityis open at one end and wherein said removable supporting means includesmeans for closing said open end of said cavity.

7. A filament supporting unit adapted for use with a gas testingapparatus having a cylindrical chamber and inlet and outlet ports incommunication with the chamber adjacent the ends thereof, said chamberhaving an open end, comprising: a plug-like member adapted for insertionin the chamber and havingan end flange adapated to close the open end ofthe chamber, said member having connected, axially spaced, circularfianges defining at least one compart-- ment intermediate the ends ofthe member, said flanges being of smaller diameter than said end flangeand defining with the wall of the cylindrical chamber restricted annularslots when said filament supporting unit is inserted in the chamber; andat least one detecting element carried by said member and disposed insaid compartment.

8. A filament supporting unit as defined in claim 7 and including acylindrical screen extending between said flanges and surrounding saiddetecting element.

9. In a gas testing apparatus of the character described, thecombination of: a cylindrical chamber having inlet and outlet portsrespectively adjacent its ends, said chamber. being open at one end; afilament supporting unit removably mounted in said chamber and removablethrough said open end of said chamber, said unit including an endportion which closes said open end of said chamber when said unit ismounted in said chamber; at least one filament carried by said unit at apoint intermediate its 20 ends; and a pair of baffles respectivelycarried by said unit on opposite sides of said filament and between saidinlet and outlet ports, said baffles co-operating with the peripheralwall of said chamber to form inlet and outlet passages for the flow ofgas into and out of the space between said baflies, said inlet andoutlet passages being-of small cross sectional area as compared to thecross sectional area of said chamber.

RALPH POOLE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 19,048 Ringrose Jan. 16, 19342,010,995 Jacobsen Aug. 13, 1935 2,197,370 Sullivan Apr. 16, 1940FOREIGN PATENTS Number Country Date 567,101 Great Britain Jan. 29, 1945

1. IN A GAS TESTING APPARATUS, THE COMBINATION OF: CASING MEANS HAVINGAN ELONGATED CAVITY THEREIN AND HAVING INLET AND OUTLET PASSAGES THEREINRESPECTIVELY COMMUNICATING WITH OPPOKSITE ENDS OF SAID CAVITY; ANIMPERFORATE INLET BAFFLE IN SAID CAVITY INTERMEDIATE SAID INLET ANDOUTLET PASSAGES AND SPACED FROM ONE END OF SAID CAVITY TO PROVIDE ANINLET CHAMBER COMMUNICAING WITH SAID INLET PASSAGE, SAID IN LET BAFFLEEXTENDING INTO CLOSE PROXIMITY TO BUT BEING SPACED FROM THE PERIPHERALWALL OF SAID CAVITY SO AS TO PROVIDE A NARROW, PERIPHERAL INLET PORTTHROUGH WHICH A GAS IN SAID INLET CHAMBER IS REQUIRED TO FLOW TO PASSSAID INLET BAFFLE; AN IMPERFORATE OUTLET BAFFLE IN SAID CAVITYINTERMEDIATE SAID INLET BAFFLE AND SAID OUTLET PASSAGE, SAID OUTLETBAFFLE BEING SPACED FROM SAID INLET BAFFLE TO PROVIDE A COMPARTMENTTHEREBETWEEN AND BEING SPACED FROM THE OTHER END OF SAID CAVITY TOPROVIDE AN OUTLET CHAMBER COMMUNICATING WITH SAID OUTLET PASSAGE, SAIDOUTLET BAFFLE EXTENDING INTO CLOSE PROXIMITY TO BUT BEING SPACED FROMTHE PERIPHERAL WALL OF SAID VACITY SO AS TO PROVIDE A NARROW, PERIPHERALOUTLET PORT THROUGH WHICH A GAS IN SAID COMPARTMENT IS REQUIRED TO FLOWTO PASS SAID OUTLET BAFFLE AND ENTER SAID OUTLET CHAMBER; MEANS FORSUPPORTING SAID BAFFLES IN SAID CAVITY; AND A FILAMENT CARRIED BY SAIDSUPPORTING MEANS AND DISPOSED IN SAID COMPARTMENT INTERMEDIATE SAIDBAFFLES.